In recent years, ad-hoc networks have been used in which the network is structured by connecting terminals to one another without using any network infrastructure such as access points of a wireless Local Area Network (LAN).
Examples of protocols used in an ad-hoc network include reactive protocols and proactive protocols that are discussed by the Mobile Ad-hoc Networks Working Group (MANET WG) in the Internet Engineering Task Force (IETF). For instance, Ad-hoc On-demand Distance Vector (AODV) is a typical example of the reactive protocols, whereas Optimized Link State Routing (OLSR) is a typical example of the proactive protocols.
In such an ad-hoc network, each of the nodes exchanges messages with other nodes that are positioned adjacent thereto so as to detect whether the adjacent nodes are each active or not and to generate a routing table. Each of the nodes then controls transfer of communication data by using the routing table generated in this manner.
Further, the wireless LAN connecting between the nodes in the ad-hoc network uses one of fourteen channels that are usable in an Industry Science Medical (ISM) band, which is a 2.4 Gigahertz band. For a wireless LAN using a plurality of channels, a technique has been disclosed by which, for example, when communication data is transmitted from a transmission origin to a transmission destination, reliability is improved by using a path formed over a plurality of channels of each node or by transmitting identical pieces of data to two or more paths.
Patent Document 1: Japanese Laid-open Patent Publication No. 2006-50371
Patent Document 2: International Publication No. 2007/029337
According to the technique described above, however, radio wave interference easily occurs because frequency bands of the channels partially overlap. Thus, a problem remains where a situation occurs in which communication interference occurs and it becomes impossible to use the communication service properly.
The problem described above will be more specifically explained, with reference to FIGS. 18 and 19. FIG. 18 is a drawing for explaining a situation in which channels are closed to one another. FIG. 19 is a drawing for explaining a situation in which communication interference is occurring. As depicted in FIG. 18, in an ad-hoc network including a gateway (GW), a node A, a node B, a node C, a node D, a node E, and a node F, the connections are made by three channels such as X (CH14), Y (CH11), and Z (CH5). In this situation, X, Y, and Z denote types of data that are communication targets of the channels, respectively. For example, when the nodes are meter apparatuses, X, Y, and Z correspond to electricity, water, and gas, respectively.
In this situation, even if it is desirable to perform communication by using CH14, because the frequency bands of the channels partially overlap, each of the nodes receives communication in the other channels. For this reason, as depicted in FIG. 19, when mutually different communication services are performed for different channels among mutually the same nodes, communication interference occurs between the channels, and it becomes impossible to use the communication services properly.